Method and apparatus for operating a diversity antenna system for communicating with implantable medical device

ABSTRACT

A far-field radio frequency (RF) telemetry system for communicating with an implantable medical device includes a diversity antenna system. Multi-frame messages each including multiple outgoing data frames are transmitted to the implantable medical device. In response, the implantable medical device transmits response data frames each following one or more of the outgoing data frames, according to a predetermined communication protocol. An antenna control circuit selects an antenna of the diversity antenna system for transmitting the outgoing data frames and/or receiving the response data frames based the quality of signal reception associated with the response data frames.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending, commonly assigned, U.S.patent application Ser. No. ______, entitled “DIVERSITY ANTENNA SYSTEMFOR COMMUNICATION WITH AN IMPLANTABLE MEDICAL DEVICE,” filed on ______(Attorney Docket No, 279.886US1) and U.S. patent application Ser. No.______, entitled “METHOD AND APPARATUS FOR ANTENNA SELECTION IN ADIVERSITY ANTENNA SYSTEM FOR COMMUNICATING WITH IMPLANTABLE MEDICALDEVICE,” filed on ______ (Attorney Docket No, 279.911US1), which arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

This document relates generally to telemetry for implantable medicalsystems and particularly to an external telemetry system havingdiversity antennas for communicating with an implantable medical device.

BACKGROUND

Medical devices are implanted in human bodies for monitoringphysiological conditions, diagnosing diseases, treating diseases, orrestoring functions of organs or tissues. Examples of such implantablemedical devices include cardiac rhythm management (CRM) devices, neuralstimulators, neuromuscular stimulators, drug delivery devices, andbiological therapy devices. When an implantable medical device isintended for long-term use in a patient, its size and power consumptionare limited by implantability and longevity requirements. Consequently,many implantable medical devices depend on external systems to performcertain functions. Communication between an implantable method deviceand an external system is performed via telemetry. Examples of specifictelemetry functions include programming the implantable medical deviceto perform certain monitoring or therapeutic tasks, extracting anoperational status of the implantable medical device, transmittingreal-time physiological data acquired by the implantable medical device,and extracting physiological data acquired by and stored in theimplantable medical device.

One type of telemetry between the implantable medical device and theexternal system is based on inductive coupling between twoclosely-placed coils using the mutual inductance between these coils.One of the coils is part of the implantable medical device, and theother coil is part of the external system. This type of telemetry isreferred to as inductive telemetry or near-field telemetry because thecoils must be closely situated for obtaining magnetically coupledcommunication.

Far-field radio-frequency (RF) telemetry provides another means forcommunications between the implantable medical device and the externalsystem. The far-field RF telemetry is performed using an RF transceiverin the implantable medical device and an RF transceiver in the externalsystem. The far-field RF telemetry frees the patient from any bodysurface attachment that limits mobility and is more suitable for usewhen the patient is at home, without the attendance by the physician orother professional caregiver.

The far-field RF telemetry between the implantable medical device andthe external system often operates in an environment where RFelectromagnetic waves are reflected from various kinds of surfaces.Destructive interference between the incident and reflective wavesresults in nulls, where the incident wave and reflected wave cancel out.The far-filed RF telemetry link is substantially interrupted when anantenna encounters a null. While such a null is moving and usuallytransient, the interruption to the telemetry link may last long enoughto cause a data transmission error.

Therefore, there is a need for ensuring the quality of far-field RFtelemetry between an external system and an implanted device when nullsare present.

SUMMARY

A far-field RF telemetry system for communicating with an implantablemedical device includes a diversity antenna system. Multi-frame messageseach including multiple outgoing data frames are transmitted to theimplantable medical device. In response, the implantable medical devicetransmits response data frames each following one or more of theoutgoing data frames, according to a predetermined communicationprotocol. An antenna control circuit selects an antenna of the diversityantenna system for transmitting the outgoing data frames and/orreceiving the response data frames based the quality of signal receptionassociated with the response data frames.

In one embodiment, a system for communicating with an implantablemedical device includes a diversity antenna system, a transceiver, anantenna interface circuit, and an antenna control circuit. The diversityantenna system includes a plurality of antennas for transmitting anoutgoing signal to the implantable medical device and receiving anincoming signal from the implantable medical device. The transceivertransmits outgoing data frames by modulating the outgoing signal andreceives incoming data frames by demodulating the incoming signal. Theantenna interface circuit includes a switch circuit that connects anantenna of the diversity antenna system to the transceiver according toan antenna selection signal. The antenna control circuit produces theantenna selection signal and includes an incoming signal monitoringtimer, an incoming signal monitoring circuit, and an antenna selector.The incoming signal monitoring timer generates incoming signalmonitoring signals based on a predetermined communication protocol. Theincoming signal monitoring circuit detects at least one measure ofquality of the incoming signal in response to each of the incomingsignal monitoring signals and produces an indication of quality of theincoming signal. The antenna selector adjusts the antenna selectionsignal based on the indication of quality of the incoming signal.

In one embodiment, a method for operating a telemetry systemcommunicating with an implantable medical device is provided. Adiversity antenna system is used for transmitting an outgoing signal tothe implantable medical device and receiving an incoming signal from theimplantable medical device. The diversity antenna includes a pluralityof antennas. Outgoing data frames are transmitted by modulating theoutgoing signal. Incoming data frames are received by demodulating theincoming signal. An antenna of the diversity antenna system is selectedto be an active antenna according to an antenna selection signal.Incoming signal monitoring signals are generated based on apredetermined communication protocol. An indication of quality of theincoming signal is produced by detecting at least one measure of qualityof the incoming signal in response to each of the incoming signalmonitoring signals. The antenna selection signal is adjusted based onthe indication of quality of the incoming signal.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects of the invention will be apparent to persons skilled in the artupon reading and understanding the following detailed description andviewing the drawings that form a part thereof. The scope of the presentinvention is defined by the appended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe similar components throughout the several views. The drawingsillustrate generally, by way of example, various embodiments discussedin the present document.

FIG. 1 is an illustration of an embodiment of a CRM system including animplantable medical device and an external system and portions of anenvironment in which the CRM system is used.

FIG. 2 is a block diagram illustrating a specific embodiment of theexternal system.

FIG. 3 is a block diagram illustrating an embodiment of a telemetrysystem of the external system.

FIG. 4 is a block diagram illustrating an embodiment of an antennacontrol circuit of the telemetry system.

FIG. 5 is a block diagram illustrating an embodiment of a responsefailure detector of the antenna control circuit of FIG. 4.

FIG. 6 is a block diagram illustrating another embodiment of the antennacontrol circuit.

FIG. 7 is a block diagram illustrating another embodiment of the antennacontrol circuit.

FIG. 8 is a block diagram illustrating another embodiment of the antennacontrol circuit.

FIG. 9 is a block diagram illustrating another embodiment of the antennacontrol circuit.

FIG. 10 is a flow chart illustrating an embodiment of a method foroperating a telemetry system communicating with an implantable medicaldevice.

FIG. 11 is a flow chart illustrating an embodiment of a method foradjusting an antenna selection signal.

FIG. 12 is a flow chart illustrating an embodiment of another method foradjusting the antenna selection signal.

FIG. 13 is a flow chart illustrating an embodiment of another method foradjusting the antenna selection signal.

FIG. 14 is a flow chart illustrating an embodiment of another method foradjusting the antenna selection signal.

FIG. 15 is a flow chart illustrating an embodiment of another method foradjusting the antenna selection signal.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description provides examples,and the scope of the present invention is defined by the appended claimsand their legal equivalents.

It should be noted that references to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.

This document discusses an RF telemetry system for bi-directionalcommunication between an implantable medical device and an externalsystem. The external system includes an external telemetry system thatuses a diversity antenna system and an antenna control circuit thatselects one or more active antenna of the diversity antenna system toensure quality of communication. In one embodiment, the antenna controlcircuit selects one or more active antenna of the diversity antennasystem for reducing or minimizing data transmission errors associatedwith nulls. An active antenna is an antenna that is currently used totransmit and/or receive signals. The antenna control circuit selects theone or more active antenna based on the quality of signal reception ofthe diversity antenna system. The signals transmitted to the implantablemedical device include multi-frame messages each including a pluralityof data frames. The implantable medical device transmits response dataframes after one or more of these transmitted data frames. The antennacontrol circuit assesses the quality of signal reception when theresponse data frames are expected to be received by the externaltelemetry system according to a communication protocol.

FIG. 1 is an illustration of an embodiment of portions of a CRM system100 and portions of an environment in which system 100 is used. System100 includes an implantable medical device 110 and an external system120. In the illustrated embodiment, after being implanted into apatient's body 101, implantable medical device 110 is coupled to thepatient's heart 102 through a lead system 105. Examples of implantablemedical device 110 include pacemakers, cardioverter/defibrillators,cardiac resynchronization therapy (CRT) devices, cardiac remodelingcontrol therapy (RCT) devices, neural stimulators, drug deliverysystems, biological therapy devices, and patient monitoring devices.External system 120 allows a physician or other caregiver to interactwith implantable medical device 110 through an RF telemetry link 115,which provides for bi-directional data communication between implantablemedical device 110 and external system 120.

RF telemetry link 115 provides for data transmission from implantablemedical device 110 to external system 120. This includes, for example,transmitting real-time physiological data acquired by implantablemedical device 110, extracting physiological data acquired by and storedin implantable medical device 110, extracting therapy history datastored in implantable medical device 110, and extracting data indicatingan operational status of implantable medical device 110 (e.g., batterystatus and lead impedance). RF telemetry link 115 also provides for datatransmission from external system 120 to implantable medical device 110.This includes, for example, programming implantable medical device 110to acquire physiological data, programming implantable medical device110 to perform at least one self-diagnostic test (such as for a deviceoperational status), and programming implantable medical device 110 todeliver at least one therapy.

RF telemetry link 115 is a far-field telemetry link. A far-field, alsoreferred to as the Fraunhofer zone, refers to the zone in which acomponent of an electromagnetic field produced by the transmittingelectromagnetic radiation source decays substantially proportionally to1/r, where r is the distance between an observation point and theradiation source. Accordingly, far-field refers to the zone outside theboundary of r=λ/2π, where λ is the wavelength of the transmittedelectromagnetic energy. In one embodiment, a communication range of RFtelemetry link 115 (a distance over which data is capable of beingwirelessly communicated) is at least ten feet but can be as long asallowed by the communication technology utilized. Unlike an inductivetelemetry link using a coil placed near implantable medical device 110,attached to the patient, and electrically connected to external system120 with a cable, using RF telemetry link 115 frees the patient from anyphysical restraints caused by the coil and the cable and allows externalsystem 120 to be placed entirely away from the sterile filed during anoperation such as the implantation of implantable medical device 110.

RF telemetry link 115 is supported by an implant telemetry system ofimplantable medical device 110 and an external telemetry system 122 ofexternal system 120. External telemetry system 122 includes a diversityantenna system 126, an antenna interface circuit 128, a transceiver 130,and an antenna control circuit 132. Diversity antenna system 126includes a plurality of antennas to transmit an outgoing signal toimplantable medical device 110 and to receive an incoming signal fromimplantable medical device 110. Antenna interface circuit 128 includestuning circuitry for diversity antenna system 126 and routes theoutgoing and incoming signals between diversity antenna system 126 andtransceiver 130. Transceiver 130 transmits outgoing data frames bymodulating the outgoing signal and receives incoming data frames bydemodulating the incoming signal. The outgoing data frames and theincoming data frames are each a frame being a logic unit of dataincluding a header, a payload, and a trailer. The header includes a“comma,” which includes a unique set of bits for signaling a receipt ofa frame. A lack of comma, or failure to receive the comma, indicates afailure to receive a frame. The payload includes the data block beingtransmitted. The trailer includes a cyclic redundancy check (CRC)character having a value generated by a transmitter. A receiver receivesthat CRC character and also recalculates the CRC character based on thereceived data block and compares the result to the received CRCcharacter in the trailer. The data is deemed to be correctly transmittedif the recalculated CRC character matches the received CRC character. ACRC error refers to a mismatch between the recalculated CRC characterand the received CRC character. Depending on the specific communicationformats, the header and the trailer each include additional informationfor flagging, control of data recovery, and/or synchronization of thereceiving device. In various embodiments, the outgoing data framesinclude multi-frame messages each including a plurality of data frames.The incoming data frames include response frames each being an incomingdata frame produced by implantable medical device 110 in response to oneor more outgoing data frames. Antenna control circuit 132 controls theoperation of antenna interface circuit for an approximately optimalperformance, or at least an acceptable performance, of diversity antennasystem 126. In various embodiments, antenna control circuit 132 selectsan active antenna of diversity antenna system 126 based on the qualityof the incoming signal. Such quality is measured by, for example,strength of the incoming signal and/or integrity of the incoming dataframes. Antenna control circuit 132 controls the timing for assessingthe quality of the incoming signal based on a predeterminedcommunication protocol according to which bi-directional communicationis performed via RF telemetry link 115. In one embodiment, antennacontrol circuit 132 selects a different active antenna of diversityantenna system 126 in response to the detection of a transmissionfailure in the incoming signal. Such a transmission failure may beassociated with a null or an antenna that is damaged or otherwise with adegraded performance. External telemetry system 122 is connected to anexternal system controller 124, which allows external system 120 toreceive information acquired by implantable medical device 110 and tocontrol the operation of implantable medical device 110. External systemcontroller 124 receives the incoming data frames from transceiver 130and sends the outgoing data frames to transceiver 130. A user interface125 allows the physician or other caregiver to view the receivedinformation and to enter commands and parameters to control theoperation of CRM system 100.

In one embodiment, external system 120 includes a programmer. In anotherembodiment, as illustrated in FIG. 2, external system 120 includes apatient management system.

FIG. 2 is a block diagram illustrating an embodiment of external system220, which is a specific embodiment of external system 120. Asillustrated in FIG. 2, external system 220 is a patient managementsystem including an external device 234, a telecommunication network236, and one or more remote devices 238. External device 234 is placedwithin the vicinity of implantable medical device 110 and includesexternal telemetry system 122 to communicate with implantable medicaldevice 110 via RF telemetry link 115. Remote device(s) 238 are in one ormore remote locations and communicates with external device 234 throughnetwork 236, thus allowing a physician or other caregiver to monitor andtreat a patient from a distant location and/or allowing access tovarious treatment resources from the one or more remote locations.

FIG. 3 is a block diagram illustrating an embodiment of an externaltelemetry system 322, which is a specific embodiment of externaltelemetry system 122. External telemetry system 322 includes a diversityantenna system 326, an antenna interface circuit 328, a transceiver 330,and an antenna control circuit 332.

Diversity antenna system 326 is a specific embodiment of diversityantenna system 126 and includes two or more antennas 340A-N. Each ofantennas 340A-N allows for transmitting an outgoing signal toimplantable medical device 110 and/or receiving an incoming signal fromimplantable medical device 110. In one embodiment, diversity antennasystem 126 includes two antennas. In a specific embodiment, the twoantennas are mounted onto a chassis of an external device such as theprogrammer or external device 234. In other embodiments, diversityantenna system 126 includes three or more antennas. One example ofdiversity antenna system 126 is discussed in U.S. patent applicationSer. No. ______, entitled. “DIVERSITY ANTENNA SYSTEM FOR COMMUNICATIONWITH AN IMPLANTABLE MEDICAL DEVICE,” filed on ______ (Attorney DocketNo, 279.886US1), which is incorporated by reference herein in itsentirety.

Antenna interface circuit 328 is a specific embodiment of antennainterface circuit 128 and includes tuning circuits 342A-N and a switchcircuit 344. Tuning circuits 342A-N each provide tuning for acorresponding antenna of antennas 342A-N. Switch circuit 344 providesfor a controllable connection between an antenna of diversity antennasystem 326 and transceiver 330 according to an antenna selection signal.This antenna is used for transmitting the outgoing signal and receivingthe incoming signal. In one embodiment, switch circuit 344 substantiallycompletes the change of the connection from between an antenna ofdiversity antenna system 326 and transceiver 330 to between anotherantenna of diversity antenna system 326 and transceiver 330 in about 50microseconds to 1 millisecond.

Transceiver 330 is a specific embodiment of transceiver 130 and includesa modulator 346 and a demodulator 348. Modulator 346 produces theoutgoing signal by modulating an RF carrier with the outgoing dataframes, including outgoing data frames that form the multi-framemessages. In one embodiment, the frequency of the RF carrier for theoutgoing signal is in a range of approximately 902 MHz to 928 MHz, withapproximately 914 MHz being a specific example. The data transmissionrate for the outgoing signal is in a range of approximately 60 kilobitsper second to 500 kilobits per second, with approximately 204.8 kilobitsper second being a specific example. Demodulator 348 recovers theincoming data frames by demodulating the received incoming signal. Theimplant telemetry circuit of implantable medical device 110 produces theincoming signal by modulating another RF carrier with the incoming dataframes. In one embodiment, the frequency of the RF carrier for theincoming signal is in a range of approximately 902 MHz to 928 MHz, withapproximately 914 MHz being a specific example. The data transmissionrate for the incoming signal is in a range of approximately 60 kilobitsper second to 500 kilobits per second, with approximately 102.4 kilobitsper second being a specific example. The incoming data frames includethe response frames each follow one or more of the outgoing data frames.In one embodiment, amplitude-shift-keying (ASK) is the modulation schemeused for both the outgoing signal and the incoming signal. Modulator 346is an ASK modulator, and demodulator 348 is an ASK demodulator.

Antenna control circuit 332 is a specific embodiment of antenna controlcircuit 132 and produces the antenna selection signal. Antenna controlcircuit 332 includes an incoming signal monitoring timer 350, anincoming signal monitoring circuit 352, and an antenna selector 354.Incoming signal monitoring timer 350 generates incoming signalmonitoring signals based on the predetermined communication protocol.The communication protocol specifies the timing for the transmission ofthe outgoing data frames and timing for the receipt of the incoming dataframes. The incoming signal monitoring signals each allow the quality ofthe incoming signal to be assessed when an incoming data frame isscheduled to be received. Incoming signal monitoring circuit 352produces an indication of the quality of the incoming signal bydetecting at least one measure of quality of the incoming signal inresponse to each of the incoming signal monitoring signals. Examples ofthe measure of quality include existence of data transmission error inthe incoming signal and strength of the incoming signal. Antennaselector 354 adjusts the antenna selection signal based on theindication of quality of the incoming signal. In one embodiment, antennaselector 354 adjusts the antenna selection signal for connecting adifferent antenna of diversity antenna system 326 to transceiver 330when an expected incoming data frame is not detected within a scheduledreception time window. In another embodiment, antenna selector 354adjusts the antenna selection signal for connecting a different antennaof diversity antenna system 326 to transceiver 330 when a transmissionerror is detected from the incoming signal. In another embodiment,antenna selector 354 adjusts the antenna selection signal for connectingan antenna of diversity antenna system 326 to transceiver 330 based thestrength of the incoming signal associated with each antenna ofdiversity antenna system 326.

FIG. 4 is a block diagram illustrating an embodiment of an antennacontrol circuit 432, which is a specific embodiment of antenna controlcircuit 332. Antenna control circuit 432 includes a nonresponsive periodtimer 456, an incoming signal monitoring timer 450, an incoming signalmonitoring circuit 452, and an antenna selector 454.

Nonresponsive period timer 456 starts a nonresponsive period during thetransmission of a multi-frame message when a response frame is expectedto be received according to the predetermined communication protocol.The multi-frame message is transmitted with an active antenna ofdiversity antenna system 326 connected to transceiver 330. The responseframe is expected to be received after several outgoing data frames ofthe multi-frame message are transmitted, according to the predeterminedcommunication protocol. The nonresponsive period is the maximum timeinterval allowed for adjusting the antenna selection signal withoutresulting in a receipt of any response frame without data transmissionerror. If the nonresponsive period expires without finding anotheractive antenna that provides for acceptable signal quality of theincoming signal, the transmission of the multi-frame message is repeatedusing a different active antenna, i.e., an antenna that is differentfrom the one with which the transmission of the multi-frame messagefirst started. In one embodiment, the nonresponsive period is apredetermined time interval in a range of approximately 50 millisecondsto one second, with approximately 100 milliseconds being a specificexample.

Incoming signal monitoring timer 450 is a specific embodiment ofincoming signal monitoring timer 350 and includes a response timer 458.Response timer 458 starts a response time interval during thetransmission of the multi-frame message when the response frame isexpected to be received and when one or more subsequent response frames,if any, are expected to be received, according to the predeterminedcommunication protocol. In other words, response timer 458 timesresponse time intervals each representing a time window during which aresponse frame is expected to be received. In one embodiment, theresponse time interval is a predetermined time interval in a range ofapproximately 4 milliseconds to 1 second, with approximately 100milliseconds being a specific example. In one embodiment, the responsetime interval is set to be equal to the interval between the end of thetransmission of an outgoing data frame and the beginning of thetransmission of the next outgoing data frame.

Incoming signal monitoring circuit 452 is a specific embodiment ofincoming signal monitoring circuit 352 and includes a response failuredetector 460. After response timer 458 starts a response time interval,response failure detector 460 detects a response failure during theresponse time interval. The response failure is a data transmissionerror associated with a response frame. Examples of such a datatransmission error include a failure to receive the response frame, afailure to receive the comma of the response frame, and a CRC error inthe response frame. Specific examples of response failure detector 460are discussed below with reference to FIG. 5.

Antenna selector 454 is a specific embodiment of antenna selector 354.During the nonresponsive period, antenna selector 454 adjusts theantenna selection signal for connecting a different antenna of diversityantenna system 326 to transceiver 330 if the response failure isdetected during the predetermined response time interval. If thenonresponsive period expires without any successful receipt of anincoming data frame during the nonresponsive period, antenna selector454 adjusts the antenna selection signal for connecting a differentantenna of diversity antenna system 326 to transceiver 330. Here thedifferent antenna refers to an antenna that is different from the onewith which the transmission of the multi-frame message started.

FIG. 5 is a block diagram illustrating an embodiment of a responsefailure detector 560, which is a specific embodiment of response failuredetector 460. In one embodiment, as illustrated in FIG. 5, responsefailure detector 560 includes a lack-of-response detector 562, alack-of-comma detector 564, and a CRC failure detector 566. In variousother embodiments, response failure detector 560 includes any one ormore of lack-of-response detector 562, lack-of-comma detector 564, andCRC failure detector 566. The response failure is detected when any oneor more of lack-of-response detector 562, lack-of-comma detector 564,and CRC failure detector 566 detect a data transmission error associatedwith the response frame. Lack-of-response detector 562 detects theresponse frame during the response time interval. The response failureis detected if no response frame is detected during the response timeinterval. Lack-of-comma detector 564 detects a comma indicative of areceipt of the response frame during the response time interval. Theresponse failure is detected if the comma is not detected during theresponse time interval. CRC failure detector 556 detects a CRC failurefrom the incoming signal during the response time interval. The responsefailure is detected if the CRC failure is detected during the responsetime interval.

In other embodiments, response failure detector 560 includes one or moreerror detectors detecting data transmission errors of types other thanthe lack of response, the lack of comma, and the CRC failure. Generally,response failure detector 560 detects any predetermined type datatransmission error in response frames, with the predetermined type datatransmission error representing the response failure.

FIG. 6 is a block diagram illustrating an embodiment of an antennacontrol circuit 632, which is another specific embodiment of antennacontrol circuit 332. Antenna control circuit 632 includes a test framegenerator 668, incoming signal monitoring timer 450, incoming signalmonitoring circuit 452, and an antenna selector 654.

Test frame generator 668 produces an antenna test signal prior to thetransmission of a multi-frame message. The antenna test signal causestransceiver 330 to transmit a test frame that is an outgoing data frame.Response timer 458 starts the response time interval following thetransmission of the test frame. Response failure detector 460 detectsthe response failure during the response time interval.

Antenna selector 654 is another specific embodiment of antenna selector354. Antenna selector 654 adjusts the antenna selection signal forconnecting a different antenna of diversity antenna system 326 totransceiver 330 when the response failure is detected during theresponse time interval. In one embodiment, test frame generator 668produces the antenna test signal for transmitting the test frame usingdifferent antennas of diversity antenna system until an antennaassociated with an acceptable quality of the incoming signal is found.In another embodiment, if a response failure is detected from anincoming signal received using an antenna, that antenna is deselected asthe only antenna associated with an unacceptable quality of the incomingsignal. If the response failure is caused by a null encountered by theantenna, the probability that a different antenna also encounters a nullis minimal. In one embodiment, test frame generator 668 produces theantenna test signal for transmitting the test frame using differentantennas of diversity antenna system until the quality of the incomingsignal is assessed for all the antennas of diversity antenna system 326.

FIG. 7 is a block diagram illustrating an embodiment of an antennacontrol circuit 732, which is another specific embodiment of antennacontrol circuit 332. Antenna control circuit 732 includes incomingsignal monitoring timer 450, incoming signal monitoring circuit 452, andan antenna selector 754. Response timer 458 times the response timeinterval when a response frame is expected to be received according tothe predetermined communication protocol. Response failure detector 460detects the response failure during the response time interval.

Antenna selector 754 is another specific embodiment of antenna selector354. Antenna selector 754 adjusts the antenna selection signal forconnecting a different antenna of diversity antenna system 326 totransceiver 330 after the transmission of a multi-frame message if theresponse failure is detected during the transmission of that multi-framemessage. Response failure detector 460 detects the response failureduring the transmission of the multi-frame message. When multipleresponse frames are expected to be received during the transmission ofthe multi-frame message, a single response failure associated with anyof the response frames causes antenna selector 754 to adjust the antennaselection signal for connecting the different antenna of diversityantenna system 326 to transceiver 330. The adjustment of the antennaselection signal occurs following the end of the transmission of themulti-frame message.

FIG. 8 is a block diagram illustrating an embodiment of an antennacontrol circuit 832, which is another specific embodiment of antennacontrol circuit 332. Antenna control circuit 832 includes a transmissionperiod timer 870, incoming signal monitoring timer 450, incoming signalmonitoring circuit 452, and an antenna selector 854.

Transmission period timer 870 times transmission periods each includinga predetermined number of the outgoing data frames. The transmissionperiod is determined based on the predetermined communication protocoland is specified by the number of the outgoing data frames. Thetransmission period is long enough such that at least one response frameis expected to be received during each transmission period. For example,if up to five consecutive outgoing data frames may be transmittedwithout expecting a response frame, the transmission period isdetermined to include at least six outgoing data frames. Response timer458 times the response time interval when a response frame is expectedto be received according to the predetermined communication protocol.Response failure detector 460 detects the response failure during theresponse time interval.

Antenna selector 854 is another specific embodiment of antenna selector354. Antenna selector 854 adjusts the antenna selection signal forconnecting a different antenna of diversity antenna system 326 totransceiver 330 at the end of each transmission period if the responsefailure is detected during that transmission period.

FIG. 9 is a block diagram illustrating an embodiment of an antennacontrol circuit 932, which is another specific embodiment of antennacontrol circuit 332. Antenna control circuit 932 includes an incomingsignal monitoring timer 950, an incoming signal monitoring circuit 952,and an antenna selector 954.

Incoming signal monitoring timer 950 is another specific embodiment ofincoming signal monitoring timer 350 and includes a signal strengthcalculation timer 972. Signal strength calculation timer 972 generates asignal strength calculation signal prior to the transmission of amulti-frame message.

Incoming signal monitoring circuit 952 is another specific embodiment ofincoming signal monitoring circuit 352 and includes a signal strengthdetector 974, a signal strength storage circuit 976, and a signalstrength calculator 978. Signal strength detector 974 measures strengthparameters each representing the strength of the incoming signalassociated with one antenna of diversity antenna system 326. In oneembodiment, signal strength detector 974 measures the strength parameterassociated with an antenna each time when that antenna is selected to bethe active antenna. Signal strength storage circuit 976 stores themeasured strength parameters. Each stored strength parameter is timestamped to indicate when the last measurement of that strength parameteris performed. Signal strength calculator 978 calculates a signalstrength index for each antenna of diversity antenna system 326 inresponse to the signal strength calculation signal. The signal strengthindex is a function of a stored strength parameter and a weightingfactor. The weighting factor is a function of the time elapsed since thelast measurement of the strength parameter. A more recently detectedstrength parameter is given more weight in the calculation of the signalstrength index.

Antenna selector 954 is another specific embodiment of antenna selector354. Antenna selector 954 adjusts the antenna selection signal forconnecting an antenna of diversity antenna system 326 to transceiver 330based on the strength indices calculated for all the antennas ofdiversity antenna system 326 in response to the signal strengthcalculation signal. In one embodiment, Antenna selector 954 adjusts theantenna selection signal to select the antenna associated with thehighest strength index.

In various embodiments, antenna control circuit 332 may combine one ormore of antenna control circuits 432, 632, 732, 832, and 932, asdetermined by one skilled in the art upon reading and understanding thisdocument. In general, an antenna control circuit assesses the quality ofthe incoming signal using any viable method and selects an antenna ofthe diversity antenna system for being the active antenna based on thequality of the incoming signal assessed for this antenna or for adifferent antenna. In various embodiments, because the probability thattwo or more antennas of the diversity antenna system simultaneouslyencounter a null is negligible, when one antenna is indicated to beassociated with unacceptable quality of the incoming signal, one or moredifferent antennas are deemed to be associated with acceptable qualityof the incoming signal.

In various embodiments, the circuits described in this document areimplemented by hardware, software, firmware, or any combination thereof.In various embodiments, the circuits or portions thereof described inthis document are each an application-specific circuit constructed toperform one or more particular functions, a general-purpose circuitprogrammed to perform such function(s), or a combination thereof.

FIG. 10 is a flow chart illustrating an embodiment of a method 1000 foroperating a telemetry system communicating with an implantable medicaldevice. In one embodiment, the telemetry system includes telemetrysystem 322.

An outgoing signal is transmitted, and an incoming signal is received,using a diversity antenna system including two or more antennas at 1010.This includes transmitting outgoing data frames to the implantablemedical device by modulating the outgoing signal and receiving incomingdata frames from the implantable medical device by demodulating theincoming signal. In various embodiments, the transmitted outgoing signalis modulated by multi-frame messages each including a plurality ofoutgoing data frames. In various embodiments, the multi-frame messageseach include two or more outgoing data frames transmitted consecutivelywithout intervening response frames.

An active antenna is selected according to an antenna selection signalat 1020. The active antenna is the antenna that is currently used totransmit the outgoing signal and/or receive the incoming signal. Theantenna selection signal specifies which antenna is active.

The antenna selection signal is adjusted based on a measure of qualityof the incoming signal at 1030. An incoming signal monitoring signal isgenerated based on a predetermined communication protocol at 1032. Thispredetermined communication protocol specifies timing of thetransmission of the outgoing data frames and timing of the receipt ofthe incoming data frames. The incoming signal monitoring signalindicates a time window within which the quality of the incoming signalis to be assessed. An indication of quality is produced for the incomingsignal associated with an antenna of the diversity antenna system at1034, in response to the incoming signal monitoring signal. Thisindication of quality is produced by detecting at least one measure ofquality of the incoming signal, such as presence of a transmission errorin the incoming signal and strength of the incoming signal. The antennaselection signal is adjusted based on the indication of quality of theincoming signal at 1036. If the quality of the incoming signal isindicated to be unacceptable, the antenna selection signal is adjustedto select a different antenna of the diversity antenna system to be theactive antenna. Exemplary specific embodiments of step 1030 arediscussed below with reference to FIGS. 11-15.

FIG. 11 is a flow chart illustrating an embodiment of a method 1100 foradjusting the antenna selection signal. Method 1100 is a specificembodiment of method 1000. In a specific embodiment, method 1100 isperformed by antenna control circuit 432.

A predetermined nonresponsive period is started at 1110, during thetransmission of a multi-frame message when a response frame is expectedto be received according to the predetermined communication protocol.The transmission of the multi-frame message is performed using a firstantenna of the diversity antenna system. The response frame is expectedto be received after two or more outgoing data frames of the multi-framemessage are transmitted using the first antenna. In one embodiment, thepredetermined nonresponsive period is in a range of approximately 50milliseconds to 1 second, with 100 milliseconds being a specificexample.

A predetermined response time interval is started at 1120, during thetransmission of the multi-frame message when the response frame isexpected to be received and when each of one or more subsequent responseframes, if any, is expected to be received. In one embodiment, thepredetermined response time interval is in a range of approximately 4milliseconds to 1 second, with approximately 100 milliseconds being aspecific example. In one embodiment, the predetermined response timeinterval is limited by the time interval between the end of thetransmission of an outgoing data frame and the beginning of thetransmission of the next outgoing data frame.

A response failure is detected during the predetermined response timeinterval at 1130. The response failure is a data transmission errorassociated with a response frame. In one embodiment, the response frameis detected during the predetermined response time interval. Theresponse failure is detected if the response frame is not detectedduring the predetermined response time interval. In another embodiment,a comma indicative of a receipt of the response frame is detected duringthe predetermined response time interval. The response failure isdetected if the comma is not detected during the predetermined responsetime interval. In another embodiment, a CRC failure in the responseframe is detected during the predetermined response time interval. Theresponse failure is detected if the CRC failure is detected during thepredetermined response time interval. In another embodiment, one or moreof the response frame, the comma, and the CRC failure are detected. Theresponse failure is detected if the response frame is not detected, orif the comma is not detected, or if the CRC failure is detected, duringthe predetermined response time interval.

The antenna selection signal is adjusted for selecting a differentantenna of the diversity antenna system to be the active antenna at1140, if the response failure is detected during the predeterminedresponse time interval. When two or more response frames are expected tobe received during the transmission of the multi-frame message, thepredetermined response time interval is started when each response frameis expected to be received, and the antenna selection signal is adjustedfor selecting a different antenna if the response failure is detectedduring the predetermined response time interval.

The antenna selection signal is adjusted for selecting a second antennaof the diversity antenna system at 1150, when the predeterminednonresponsive period expires without successful receipt of any responseframe. The second antenna is an antenna different from the firstantenna. That is, if none of the incoming data frames is receivedwithout the data transmission error during the predeterminednonresponsive period, a different antenna is selected for repeating thetransmission of the multi-frame message or performing the transmissionof another multi-frame message.

FIG. 12 is a flow chart illustrating an embodiment of a method 1200 foradjusting the antenna selection signal. Method 1200 is another specificembodiment of method 1000. In a specific embodiment, method 1200 isperformed by antenna control circuit 632.

An antenna test signal is produced at 1210, prior to the transmission ofthe multi-frame message. The antenna test signal cause a test frame tobe transmitted to the implantable medical device, which transmits aresponse frame after receiving the test frame. The predeterminedresponse time interval is started at 1220, following the transmission ofthe test frame. The response failure is detected during thepredetermined response time interval at 1230. The antenna selectionsignal is adjusted for selecting a different antenna of the diversityantenna system to be the active antenna when the response failure isdetected at 1240. In one embodiment, method 1200 is repeated for all theantennas of the diversity antenna system. In another embodiment, method1200 is repeated with another antenna only if the response failure isdetected with the currently active antenna. In another embodiment, ifthe response failure is detected with the currently active antenna, adifferent antenna is assumed to be associated with acceptable quality ofthe incoming signal and is therefore selected.

FIG. 13 is a flow chart illustrating an embodiment of a method 1300 foradjusting the antenna selection signal. Method 1300 is another specificembodiment of method 1000. In a specific embodiment, method 1300 isperformed by antenna control circuit 732.

The predetermined response time interval is started at 1310, during thetransmission of the multi-frame message when a response frame isexpected to be received. The response failure is detected during thepredetermined response time interval at 1320. The antenna selectionsignal is adjusted for selecting a different antenna of the diversityantenna system to be the active antenna after the transmission of themulti-frame message if the response failure is detected during thetransmission of the multi-frame message at 1330. When two or moreresponse frames are expected to be received during the transmission ofthe multi-frame message, a single response failure associated with anyof the response frames causes the antenna selection signal to beadjusted for selecting the different antenna to be the active antenna.

FIG. 14 is a flow chart illustrating an embodiment of a method 1400 foradjusting the antenna selection signal. Method 1400 is another specificembodiment of method 1000. In a specific embodiment, method 1400 isperformed by antenna control circuit 832.

A transmission period is timed at 1410. The transmission period includesa period during which a predetermined number of the outgoing data framesare transmitted. The transmission period is timed repeatedly while theoutgoing data frames are transmitted to the implantable medical device.The number of the outgoing data frames in the transmission period isdetermined based on the predetermined communication protocol. At leastone response frame is expected to be received during each transmissionperiod. The predetermined response time interval is started at 1420,during the transmission period when a response frame is expected to bereceived. The response failure is detected during the predeterminedresponse time interval at 1430. The antenna selection signal is adjustedfor selecting a different antenna of the diversity antenna system to bethe active antenna at 1440, at the end of the transmission period if theresponse failure is detection during the transmission period.

FIG. 15 is a flow chart illustrating an embodiment of a method 1500 foradjusting the antenna selection signal. Method 1500 is another specificembodiment of method 1000. In a specific embodiment, method 1500 isperformed by antenna control circuit 932.

Strength parameters each associated with an antenna are measured at1510. The strength parameters each represent strength of the incomingsignal received by one antenna of the diversity antenna system. Examplesof the strength parameter include amplitude and power of the incomingsignal. The strength parameters are stored at 1520. Each stored strengthparameter is time stamped to indicate when that strength parameter wasmeasured. Prior to the transmission of a multi-frame message, a signalstrength calculation signal is generated at 1530. In response to thesignal strength calculation signal, signal strength indices arecalculated at 1540. The signal strength indices are each associated withone antenna of the diversity antenna system and is calculated based onthe strength parameter and a weighting factor. The weighting factor is afunction of the time elapsed since the measurement of the strengthparameter. The antenna selection signal is adjusted for selecting anantenna of the diversity antenna system to be the active antenna basedon the signal strength indices at 1550. In one embodiment, the antennaselection signal is adjusted for selecting the antenna associated withthe highest signal strength index, i.e., associated with the strongestincoming signal strength as recently measured.

Methods 1100, 1200, 1300, 1400, and 1500 are exemplary specificembodiments illustrating how the assessment of the quality of theincoming signal is timed and performed and how the antenna selectionsignal is adjusted based on the assessed quality of the incoming signal.In various embodiments, these specific embodiments may be combined, andother specific embodiments may be employed, as determined by one skilledin the art upon reading and understanding this document. In general, thequality of the incoming signal is assessed using any viable method, andan antenna of the diversity antenna system is selected for being theactive antenna based on the quality of the incoming signal assessed forthis antenna or for a different antenna.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. For example, the implantablemedical device can be any implantable medical device capable ofcommunicating with an external system or device via RF telemetry. Manyother embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the invention should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled.

1. A system for communicating with an implantable medical device, thesystem comprising: a diversity antenna system including a plurality ofantennas configured to transmit an outgoing signal to the implantablemedical device and to receive an incoming signal from the implantablemedical device; a transceiver adapted to transmit outgoing data framesby modulating the outgoing signal and to receive incoming data frames bydemodulating the incoming signal; an antenna interface circuit coupledbetween the diversity antenna system and the transceiver, the antennainterface circuit including a switch circuit adapted to connect anantenna of the diversity antenna system to the transceiver according toan antenna selection signal; and an antenna control circuit adapted toproduce the antenna selection signal, the antenna control circuitincluding: an incoming signal monitoring timer adapted to generateincoming signal monitoring signals based on a predeterminedcommunication protocol; an incoming signal monitoring circuit coupled tothe incoming signal monitoring timer, the incoming signal monitoringcircuit adapted to produce an indication of quality of the incomingsignal by detecting at least one measure of quality of the incomingsignal in response to each of the incoming signal monitoring signals;and an antenna selector coupled to the incoming signal monitoringcircuit and the switch circuit, the antenna selector adapted to adjustthe antenna selection signal based on the indication of quality of theincoming signal.
 2. The system of claim 1, wherein the switch circuit isadapted to connect the antenna of the diversity antenna system to thetransceiver for transmitting the outgoing signal and receiving theincoming signal.
 3. The system of claim 1, wherein the transceiver isadapted to transmit multi-frame messages each including a plurality ofdata frames of the outgoing data frames.
 4. The system of claim 3,wherein the incoming signal monitoring timer comprises a response timerto start a predetermined response time interval when a response frame isexpected to be received according to the predetermined communicationprotocol, the response frame being one of the incoming data frames andresponding to one or more frames of the outgoing data frames transmittedto the implantable medical device, and wherein the incoming signalmonitoring circuit comprises a response failure detector adapted todetect a response failure during the predetermined response timeinterval, the response failure being a data transmission errorassociated with the response frame.
 5. The system of claim 4, whereinthe response failure detector comprises a lack-of-response detectoradapted to detect the response frame during the predetermined responsetime interval, and the response failure is detected if the responseframe is not detected during the predetermined response time interval.6. The system of claim 4, wherein the response failure detectorcomprises a lack-of-comma detector adapted to detect a comma indicativeof a receipt of the response frame during the predetermined responsetime interval, and the response failure is detected if the comma is notdetected during the predetermined response time interval.
 7. The systemof claim 4, wherein the response failure detector comprises a cyclicredundancy check (CRC) failure detector adapted to detect a CRC failurein the response frame during the predetermined response time interval,and the response failure is detected if the CRC failure is detectedduring the predetermined response time interval.
 8. The system of claim4, wherein the antenna control circuit further comprises a nonresponsiveperiod timer to start a predetermined nonresponsive period during atransmission of one of the multi-frame messages with a first antenna ofthe diversity antenna system connected to the transceiver when theresponse frame is expected to be received, and wherein the responsetimer is adapted to start the predetermined response time intervalduring the transmission of the one of the multi-frame messages when theresponse frame is expected to be received and when each of one or moresubsequent response frames is expected to be received, the subsequentresponse frame each being one of the incoming data frames and respondingto one or more frames of the outgoing data frames transmitted to theimplantable medical device.
 9. The system of claim 8, wherein theantenna selector is adapted to adjust the antenna selection signal forconnecting a different antenna of the diversity antenna system to thetransceiver if the response failure is detected during the predeterminedresponse time interval and adapted to adjust the antenna selectionsignal for connecting a second antenna of the diversity antenna systemto the transceiver when the predetermined nonresponsive period expiresif none of the incoming data frames is received without the datatransmission error during the predetermined nonresponsive period. 10.The system of claim 4, wherein the antenna control circuit furthercomprises a test frame generator to produce an antenna test signalcausing the transceiver to transmit a test frame of the outgoing dataframes prior to a transmission of one of the multi-frame messages, andwherein the response timer is adapted to start the predeterminedresponse time interval following the transmission of the test frame. 11.The system of claim 10, wherein the antenna selector is adapted toadjust the antenna selection signal for connecting a different antennaof the diversity antenna system to the transceiver if the responsefailure is detected during the predetermined response time interval. 12.The system of claim 4, wherein the response timer is adapted to startthe predetermined response time interval during a transmission of one ofthe multi-frame messages when the response frame is expected to bereceived.
 13. The system of claim 12, wherein the antenna selector isadapted to adjust the antenna selection signal for connecting adifferent antenna of the diversity antenna system to the transceiverafter the transmission of the one of the multi-frame messages if theresponse failure is detected during the transmission of the one of themulti-frame messages.
 14. The system of claim 4, wherein the antennacontrol circuit further comprises a transmission period timer to timetransmission periods each including a period during which apredetermined number of data frames of the outgoing data frames aretransmitted, and wherein the response timer is adapted to start thepredetermined response time interval during each of the transmissionperiods when the response frame is expected to be received.
 15. Thesystem of claim 14, wherein the antenna selector is adapted to adjustthe antenna selection signal for connecting a different antenna of thediversity antenna system to the transceiver at an end of the each of thetransmission periods if the response failure is detected during the eachof the transmission periods.
 16. The system of claim 3, wherein theincoming signal monitoring timer includes a signal strength calculationtimer adapted to generate a signal strength calculation signal prior toa transmission of one of the multi-frame messages.
 17. The system ofclaim 16, wherein the incoming signal monitoring circuit comprises: asignal strength detector to measure strength parameters eachrepresentative of strength of the incoming signal associated with oneantenna of the diversity antenna system; a signal strength storagecircuit to store the strength parameters; and a signal strengthcalculator to calculate signal strength indices each associated with oneantenna of the diversity antenna system based on the strength parametersand weighting factors each associated with one of the strengthparameters and related to a timing of the measurement of that one of thestrength parameters in response to the signal strength calculationsignal.
 18. The system of claim 17, wherein the antenna selector isadapted to adjust the antenna selection signal for connecting an antennaof the diversity antenna system to the transceiver based on the signalstrength indices.
 19. A method for operating a telemetry systemcommunicating with an implantable medical device, the method comprising:transmitting an outgoing signal to the implantable medical device andreceiving an incoming signal from the implantable medical device using adiversity antenna system including a plurality of antennas, whereintransmitting the outgoing signal includes transmitting outgoing dataframes by modulating the outgoing signal, and receiving the incomingsignal includes receiving incoming data frames by demodulating theincoming signal; selecting an antenna of the diversity antenna system tobe an active antenna according to an antenna selection signal, theactive antenna used for transmitting the outgoing signal and receivingthe incoming signal; generating incoming signal monitoring signals basedon a predetermined communication protocol; producing an indication ofquality of the incoming signal by detecting at least one measure ofquality of the incoming signal in response to each of the incomingsignal monitoring signals; and adjusting the antenna selection signalbased on the indication of quality of the incoming signal.
 20. Themethod of claim 19, wherein transmitting the outgoing data framescomprises transmitting multi-frame messages each including a pluralityof data frames of the outgoing data frames.
 21. The method of claim 20,wherein generating the incoming signal monitoring signals comprisesstarting a predetermined response time interval when a response frame isexpected to be received according to the predetermined communicationprotocol, the response frame being one of the incoming data frames andresponding to one or more frames of the outgoing data frames transmittedto the implantable medical device, and wherein detecting the at leastone measure of quality of the incoming signal comprises detecting aresponse failure during the predetermined response time interval, theresponse failure being a data transmission error associated with theresponse frame.
 22. The method of claim 21, wherein detecting theresponse failure comprises detecting the response frame during thepredetermined response time interval, and wherein the response failureis detected if the response frame is not detected during thepredetermined response time interval.
 23. The method of claim 21,wherein detecting the response failure comprises detecting a commaindicative of a receipt of the response frame during the predeterminedresponse time interval, and wherein the response failure is detected ifthe comma is not detected during the predetermined response timeinterval.
 24. The method of claim 21, wherein detecting the responsefailure comprises detecting a cyclic redundancy check (CRC) failure inthe response frame during the predetermined response time interval, andwherein the response failure is detected if the CRC failure is detectedduring the predetermined response time interval.
 25. The method of claim21, further comprising starting a predetermined nonresponsive periodduring a transmission of one of the multi-frame messages using a firstantenna of the diversity antenna system selected to be the activeantenna when the response frame is expected to be received, and whereinstarting the predetermined response time interval comprises starting thepredetermined response time interval during the transmission of the oneof the multi-frame messages when the response frame is expected to bereceived and when each of one or more subsequent response frames isexpected to be received, the one or more subsequent response frames eachbeing one of the incoming data frames and responding to one or moreframes of the outgoing data frames transmitted to the implantablemedical device.
 26. The method of claim 25, wherein adjusting theantenna selection signal comprises adjusting the antenna selectionsignal for selecting a different antenna of the diversity antenna systemto be the active antenna if the response failure is detected during thepredetermined response time interval.
 27. The method of claim 26,wherein adjusting the antenna selection signal further comprisesadjusting the antenna selection signal for selecting a second antenna ofthe diversity antenna system to be the active antenna when thepredetermined nonresponsive period expires if none of the incoming dataframes is received without the data transmission error during thepredetermined nonresponsive period.
 28. The method of claim 21, furthercomprising producing an antenna test signal causing a transmission of atest frame of the outgoing data frames prior to a transmission of one ofthe multi-frame messages, and wherein starting the predeterminedresponse time interval comprises starting the predetermined responsetime interval following the transmission of the test frame.
 29. Themethod of claim 28, wherein adjusting the antenna selection signalcomprises adjusting the antenna selection signal for selecting adifferent antenna of the diversity antenna system to be the activeantenna when the response failure is detected during the predeterminedresponse time interval.
 30. The method of claim 21, wherein starting thepredetermined response time interval comprises starting thepredetermined response time interval during a transmission of one of themulti-frame messages when the response frame is expected to be received.31. The method of claim 30, wherein adjusting the antenna selectionsignal comprises adjusting the antenna selection signal for selecting adifferent antenna of the diversity antenna system to be the activeantenna after the transmission of the one of the multi-frame messages ifthe response failure is detected during the transmission of the one ofthe multi-frame messages.
 32. The method of claim 21, further comprisingtiming transmission periods each including a period during which apredetermined number of data frames of the outgoing data frames aretransmitted, and wherein starting the predetermined response timeinterval comprises starting the predetermined response time intervalduring each of the transmission periods when the response frame isexpected to be received.
 33. The method of claim 32, wherein adjustingthe antenna selection signal comprises adjusting the antenna selectionsignal for selecting a different antenna of the diversity antenna systemto be the active antenna at an end of the each of the transmissionperiods if the response failure is indicated during the each of thetransmission periods.
 34. The method of claim 20, wherein generating theincoming signal monitoring signals comprises generating a signalstrength calculation signal prior to a transmission of one of themulti-frame messages.
 35. The method of claim 34, wherein producing theindication of quality of the incoming signal comprises: measuringstrength parameters each representative of strength of the incomingsignal associated with one antenna of the diversity antenna system;storing the measured strength parameters; and calculating signalstrength indices each associated with one antenna of the diversityantenna system based on the strength parameters and weighting factorseach associated with one of the strength parameters and related to atiming of the measurement of that one of the strength parameters inresponse to the signal strength calculation signal.
 36. The method ofclaim 35, wherein adjusting the antenna selection signal comprisesadjusting the antenna selection signal for selecting an antenna of thediversity antenna system to be the active antenna based on the signalstrength indices.